"Plotz will create a hollow sphere (and now wizard towers and observatory models) of your chosen size and you can then step through the layers to see how to build it. Plotz will also print a full schematic including a 'ghost' of the layer below to help you position blocks."

Mike Farley has created a fantastic resource for teachers of social studies here. Under the headings: Energy, Environment, Global Poverty, Global Conflict, Migration & Civic Action, he has provided links to 'serious games', together with downloadable worksheets that aim to help students get the most out of the game.